Method and apparatus for operating traveling spark igniter at high pressure

Abstract

An ignition circuit and a method of operating an igniter (preferably a traveling spark igniter) in an internal combustion engine, including a high pressure engine. A high voltage is applied to electrodes of the igniter, sufficient to cause breakdown to occur between the electrodes, resulting in a high current electrical discharge in the igniter, over a surface of an isolator between the electrodes, and formation of a plasma kernel in a fuel-air mixture adjacent said surface. Following breakdown, a sequence of one or more lower voltage and lower current pulses is applied to said electrodes, with a low “simmer” current being sustained through the plasma between pulses, preventing total plasma recombination and allowing the plasma kernel to move toward a free end of the electrodes with each pulse.

What is claimed is: 
     
       1. A method of plasma generation, comprising:
 a. applying, to an igniter having at least a pair of electrodes, a voltage of amplitude sufficient to cause breakdown to occur between the electrodes, resulting in a pulse of high current electrical discharge in the igniter in an initiation region between the pair of electrodes, and formation of a plasma kernel adjacent said initiation region; 
 b. switching a switching element, in response to a signal from a pulse generator, to draw at least most of the pulse of high current electrical discharge from between the pair of electrodes of the igniter through the switching element; and 
 c. switching the switching element off while current therethrough is not zero. 
 
     
     
       2. The method of  claim 1 , further comprising, following breakdown, switching the switching element to apply to said electrodes at least one follow-on pulse by discharging a plasma-sustaining capacitor in response to a signal from the pulse generator. 
     
     
       3. The method of  claim 2 , wherein:
 one or more of the at least one follow-on pulse are voltage pulses generated by the plasma-sustaining capacitor pulling its discharge current through an inductance; and 
 the inductance is in series with the plasma-sustaining capacitor and inductively coupled to a second inductance that is in series with one of the electrodes. 
 
     
     
       4. The method of  claim 3 , wherein the inductance is further in series with a second switching element that modulates a discharge current of the plasma-sustaining capacitor. 
     
     
       5. The method of  claim 1 , wherein the switching element is of a type that can be switched while the current therethrough is not constant. 
     
     
       6. The method of  claim 1 , wherein the switching element is switched on a plurality of times, each time to draw at least most of a respective pulse of high current electrical discharge from the igniter through the switching element, and wherein the switching element is switched off at least once between the plurality of times the switching element is switched on. 
     
     
       7. The method of  claim 1 , wherein switching the switching element draws all of the pulse of high current electrical discharge from between the pair of electrodes of the igniter through the switching element. 
     
     
       8. The method of  claim 1 , wherein switching the switching element draws most of the pulse of high current electrical discharge from between the pair of electrodes of the igniter through the switching element. 
     
     
       9. The method of  claim 8 , wherein switching the switching element draws, through the switching element, all of the pulse of high current electrical discharge beyond simmer current used to avoid total plasma recombination between the pair of electrodes. 
     
     
       10. The method of  claim 1 , further comprising:
 discharging a plasma-sustaining capacitor to cause at least most of the pulse of high current electrical discharge in the igniter, 
 wherein switching the switching element draws, through the switching element, all of the pulse of high current electrical discharge caused by discharging the plasma-sustaining capacitor. 
 
     
     
       11. The method of  claim 1 , wherein the switching element is in series with an inductance that is coupled to the pair of electrodes, and the switching element is configured to draw, through the switching element, all of the pulse of high current electrical discharge that passes through the inductance. 
     
     
       12. A circuit for plasma generation, the circuit comprising:
 an igniter having at least a pair of electrodes and configured to have applied thereto a voltage of amplitude sufficient to cause breakdown to occur between the electrodes, resulting in a pulse of high current electrical discharge in the igniter in an initiation region between the pair of electrodes, and formation of a plasma kernel adjacent said initiation region; and 
 a switching element configured to:
 switch, in response to a signal from a pulse generator, to draw at least most of the pulse of high current electrical discharge from between the pair of electrodes of the igniter through the switching element; and 
 be switched off while current therethrough is not zero. 
 
 
     
     
       13. The circuit of  claim 12 , further comprising:
 a plasma-sustaining capacitor, 
 wherein the switching element is further configured to, following breakdown, apply to the electrodes at least one follow-on pulse by discharging the plasma-sustaining capacitor in response to a signal from the pulse generator. 
 
     
     
       14. The circuit of  claim 13 , wherein:
 one or more of the at least one follow-on pulse are voltage pulses generated by the plasma-sustaining capacitor pulling its discharge current through an inductance; and 
 the inductance is in series with the plasma-sustaining capacitor and inductively coupled to a second inductance that is in series with one of the electrodes. 
 
     
     
       15. The circuit of  claim 14 , wherein the inductance is further in series with a second switching element configured to modulate a discharge current of the plasma-sustaining capacitor. 
     
     
       16. The circuit of  claim 12 , wherein the igniter is a traveling spark igniter. 
     
     
       17. The circuit of  claim 12 , wherein the switching element is of a type that can be switched while the current therethrough is not constant. 
     
     
       18. The circuit of  claim 12 , wherein the pulse generator is configured to switch the switching element on a plurality of times, each time to draw at least most of a respective pulse of high current electrical discharge from the igniter through the switching element and to switch the switching element off at least once between the plurality of times the switching element is switched on. 
     
     
       19. The circuit of  claim 12 , wherein the switching element is coupled in series with the pair of electrodes of the igniter to receive at least most of the pulse of high current electrical discharge from the igniter. 
     
     
       20. The circuit of  claim 12 , wherein the switching element is configured to draw all of the pulse of high current electrical discharge from between the pair of electrodes of the igniter through the switching element. 
     
     
       21. The circuit of  claim 12 , wherein the switching element is configured to draw most of the pulse of high current electrical discharge from between the pair of electrodes of the igniter through the switching element. 
     
     
       22. The circuit of  claim 21 , wherein the switching element is configured to draw, through the switching element, all of the pulse of high current electrical discharge beyond simmer current used to avoid total plasma recombination between the pair of electrodes. 
     
     
       23. The circuit of  claim 12 , further comprising:
 a plasma-sustaining capacitor to cause at least most of the pulse of high current electrical discharge in the igniter, 
 wherein the switching element is configured to:
 cause the plasma-sustaining capacitor to discharge at least most of the pulse of high current electrical discharge in the igniter; and 
 draw, through the switching element, all of the pulse of high current electrical discharge caused by discharging the plasma-sustaining capacitor. 
 
 
     
     
       24. The circuit of  claim 12 , further comprising:
 an inductance coupled to the pair of electrodes, 
 wherein the switching element is in series with the inductance and configured to draw, through the switching element, all of the pulse of high current electrical discharge that passes through the inductance.